Support AIS type 6 FAC 235 FI 10

[pierregarreau]

From the documentation, these message types are used to "provides AtoN (Aid to navigation) monitoring data for the General Lighthouse Authorities (GLA), which consists of Trinity House (England & Wales), Northern Lighthouse Board (Scotland) and the Commissioners of Irish Lights (Ireland)."

An example message is:

!AIVDM,1,1,4,B,6>jR0600V:C0>da4P106P00,2*02

and can be decoded as:

{
  'id': 6,
  'repeat_indicator': 0,
  'mmsi': 992509976,
  'seq': 0,
  'mmsi_dest': 2500912,
  'retransmit': True,
  'spare': 0,
  'dac': 235,
  'fi': 10,
  'ana_int': 274,
  'ana_ext1': 1,
  'ana_ext2': 1,
  'racon': 2,
  'light': 2,
  'health': False,
  'stat_ext': 0,
  'off_pos': False,
  'spare2': 0
}